Salt-dependent expression of ammonium assimilation genes in the halotolerant yeast, Debaryomyces hansenii

Abstract

Debaryomyces hansenii is adapted to grow in saline environments, accumulating high intracellular Na(+) concentrations. Determination of the DhGDH1-encoded NADP-glutamate dehydrogenase enzymatic activity showed that it increased in a saline environment. Thus, it was proposed that, in order to overcome Na(+) inhibition of enzyme activity, this organism possessed salt-dependent mechanisms which resulted in increased activity of enzymes pertaining to the central metabolic pathways. However, the nature of the mechanisms involved in augmented enzyme activity were not analyzed. To address this matter, we studied the expression of DhGDH1 and DhGLN1 encoding glutamine synthetase, which constitute the central metabolic circuit involved in ammonium assimilation. It was found that: (1) expression of DhGDH1 is increased when D. hansenii is grown in the presence of high NaCl concentrations, while that of DhGLN1 is reduced, (2) DhGDH1 expression in Saccharomyces cerevisiae takes place in a GLN3- and HAP2,3-dependent manner and (3) salt-dependent DhGDH1 and DhGLN1 expression involves mechanisms which are limited to D. hansenii and are not present in S. cerevisiae. Thus, salt-dependent regulation of the genes involved in central metabolic pathways could form part of a strategy leading to the ability to grow under hypersaline conditions.

Cell wall involvement in the glycerol response to high osmolarity in the halotolerant yeast Debaryomyces hansenii

“…In the literature four genes have been reported to be salt-responsive in D. hansenii: DhGPD1, DhENA1, DhENA2 and DhGDH1 (Thomé and Trench 1998;Almagro et al 2001;Guerrero et al 2005). It has been shown that GPD1 in S. cerevisiae is modulated by the HOG pathway and is directly involved in the osmoregulated response in yeasts (Hohmann 2002).…”

“…cerevisiae (Guerrero et al 2005). In the present work DhGPD1 was chosen as a gene marker to study the glycerol response to turgor stress, while DhGDH1 was chosen as a control for the saltresponse in this yeast.…”

“…It is interesting that DhGDH1 responded to turgor/hydric stress in a similar way to DhGPD1, since the activity of the enzyme encoded by this gene is not directly involved in the modulation of the intracellular osmotic pressure. In S. cerevisiae DhGDH1 is not salt-induced, suggesting that D. hansenii may contain specific regulatory networks not present in S. cerevisiae (Guerrero et al 2005).…”

“…The DhGPD1-specific probe was prepared by PCR amplification of a 1 Kb central fragment using primers specific for D. hansenii (Thomé 2004). DhGDH probe was a kind gift of Dr. Alicia Gonzá lez (IFC, UNAM) prepared also by PCR (Guerrero et al 2005). 17S rDNA derived probe was amplified using specific primers according to the Genolevures sequence.…”

Performance of indigenous yeasts in the processing of Chinese strong-flavoured liquor during spontaneous mixed solid-state or submerged fermentation

“…Debaryomyces hansenii and Wickerhamomyces anomalus strains were found to be predominantly distributed, whereas Lodderomycese longisporus strains, Zygosaccharomyces bailii, Pichia kudriavzevii, Pichia manshurica, Trichosporonoides spathulata and several unidentified species were subordinated. These yeast species have been isolated from wine or other fermentation processes (6) and studied from the perspectives of metabolism, genetics, and molecular biology (7)(8)(9)(10)(11)(12)(13). Particular stains of Debaryomyces hansenii, Wickerhamomyces anomalus, Pichia kudriavzevii and Pichia manshurica have been found to promote volatile compound formation (14)(15)(16)(17).…”